Mono-Team or Elemental Advantage?

[Kazuto9x]

Thanks to some guy's in this forum, I am really confused now!
I started last week to play Kamihime Project and my main element is Water because of Cthullu and Ryu-Oh.
I also have a second Account with Gaia, Titania and Sol because of Water's elemental disadvantage against thunder.

Since yesterday I don't know exactly what to do now
1. Should I focus at the moment in my main team? Or just get every weapon, Eideleon, SR Event Hime's and build a team for each element?
2. Are miracle tickets even worth if I just need elemental advantage? Should I just get Sol for heal and use the SR Hime's from events and gatcha rolls.
3. Do I even need -50% debuffs with elemental advantage? Because I don't think I will get for each element a -50% debuff...
4. What is this Tower exactly? And why do people say that mono-element user will have a hard time? I am not planning to do every Ragnarok for each element solo...
5. Then isn't it better to make a Dark/Light account because they have a little advantage against each element?
FURTHERMORE in each event I am collecting all SSR weapon's, maybe I need those someday in the future.